This invention relates to fuel injection systems for diesel engines.
Typical common rail fuel injection systems have one localized high pressure fuel pump connected by serially connected inlet and outlet lines which carry high pressure fuel between the injectors and the fuel pump. The lines connecting to the fuel pump are single or double walled depending upon the application. Double walled fuel lines are currently used to provide additional leak protection around the inner fuel line. Specifically, the inner line is used to carry pressurized fuel while the outer line is kept dry to form an extra barrier between the inner fuel line and the high temperature surfaces in an engine.
The present invention provides a common rail diesel fuel injection system. The system uses a double walled fuel line having a high pressure inner fuel tube for delivering high pressure fuel from a fuel pump to a series of fuel injectors, and a low pressure outer fuel tube for returning low pressure fuel from the fuel injectors to the fuel pump or the fuel tank. The outer line surrounds the inner line and prevents leaks in the inner line from escaping into the engine compartment. The double walled fuel line provides an additional barrier of protection between the high pressure inner line and the engine as well as a convenient path for fuel flow both to and from the injectors.
Sensing fuel leaks in the system may be accomplished by monitoring fuel pressure in the low pressure fuel line and comparing it against a map of predetermined normal pressures. If a leak occurs in the outer line, the pressure in the line will drop below normal because of lost fuel. If a leak occurs in the inner line, high pressure fuel will flow into the low pressure outer line, increasing fuel pressure in the outer line. Therefore, an increase or decrease in the normal return fuel pressure in the outer line will indicate that there is a leak and whether it is in the inner or the outer line.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.